Cough is a frequent complaint of COPD (chronic obstructive pulmonary disease) patients (and other patients) that can significantly impact quality of life at both a functional and a nuisance level. It is expected that understanding cough in disease progression and treatment will enable more targeted treatments and better understanding of the patient's disease experience. However, true cough frequency and its circadian distribution remain relatively unknown because it has been difficult to objectively quantify cough in the ‘real world environment’ for a number of technical reasons leaving. Objective quantification of cough by other routine has been difficult and time consuming for both researchers and subjects.
Moreover, the art lacks portable and easy-to-use monitoring methods and systems that provide objective and quantitative data on cough and, for cough during sleep, accompanying EEG arousals. In the inventor(s) experience, no portable device has heretofore demonstrated an ability to recognize coughs and to monitor cough frequency or to provide concurrent cough and EEG data. Although a number of portable devices for assessing daytime and night time cough have been reported, none has been reported to assess night time cough together with its influence on sleep architecture as revealed by electroencephalography (EEG). See, e.g., Cox et al., 1984, An electromyographic method of objectively assessing cough intensity and use of the method to assess effects of codeine on the dose-response curve to citric acid. British Journal of Clinical Pharmacology 18: 377-382, 1984; Munyard et al., 1994, A new device for ambulatory cough recording. Pediatric Pulmonology 18: 178-186, 1994; and Subburaj et al., 1996, Methods of recording and analyzing cough sounds. Pulmonary Pharmacology 9: 269-279, 1996.
Considerable confusion in the art has resulted from this lack of objective methods and systems for monitoring cough and sleep. On one hand, it has been previously reported that sleep suppresses cough. See, e.g., Hsu et al., Coughing frequency in patients with persistent cough: assessment using a 24 hour ambulatory recorder. European Respiratory Journal 7: 1246-1253, 1994. Studies from EEG laboratories have reported that cough is almost completely absent in stage 3 and 4 sleep (deep sleep) and is further not thought to be accompanied by night time awakenings. See, e.g., Power et al., 1984, Nocturnal cough in patients with chronic bronchitis and emphysema. American Review of Respiratory Disease 130: 999-1001, 1984. On the other hand, it has also been reported that the nocturnal cough and wheezing associated with asthma may impact sleep quality. In the study of Selby et al., 1997, Inhaled salmeterol or oral theophylline in nocturnal asthma? American Journal of Respiratory & Critical Care Medicine 155: 104-108, 1997, patients either received 50 μg salmeterol or individually dose-titrated sustained-release oral theophylline. Post salmeterol treatment, patients reported an improved quality of life. The authors did observe fewer nocturnal arousals, but they did not indicate whether the arousals were due to airway obstruction or to cough. Sleep architecture did not appear to differ pre/post treatment.
On the other hand, others report that sleep in patients with a number of sleep disorders, pulmonary disorders, and in some elderly is punctuated with frequent, brief arousals. The arousals are transient and generally do not result in behavioral awakening, reoccurring in some conditions as often as once per minute. The arousing stimulus differs in the various disorders and can be identified in some cases (i.e. cough, apnea, leg movements, pain), whereas in other cases (i.e. “normal” sleep of elderly, some insomnias) it is idiopathic. EEG data during sleep reveals patients arouse to cough. Thus, multiple cough bouts over the course of the night yield multiple arousals and, therefore, may ultimately influence over all sleep quality. The important fact is that the arousals result in fragmented sleep rather than shortened sleep. Just as with shortened sleep, it now is clear that sleep fragmentation leads to increased daytime sleepiness and other deleterious effects.
This lack of objective and quantitative cough and sleep monitoring methods and systems has thus led to confusion in the art and has hindered management of COPD, asthma, and similar conditions. Such methods and systems would therefore benefit medical research and medical practice.
A number of references are cited herein, the entire disclosures of which are incorporated herein, in their entirety, by reference for all purposes. Further, none of these references, regardless of how characterized above, is admitted as prior to the invention of the subject matter claimed herein.